Move client-specific files to 'src/client' (#7902)

Update Android.mk
Remove 'src/client' from include_directories

src/client/imagefilters.h

@@ -0,0 +1,43 @@
+/*
+Copyright (C) 2015 Aaron Suen <warr1024@gmail.com>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#pragma once
+
+#include "irrlichttypes_extrabloated.h"
+
+/* Fill in RGB values for transparent pixels, to correct for odd colors
+ * appearing at borders when blending.  This is because many PNG optimizers
+ * like to discard RGB values of transparent pixels, but when blending then
+ * with non-transparent neighbors, their RGB values will shpw up nonetheless.
+ *
+ * This function modifies the original image in-place.
+ *
+ * Parameter "threshold" is the alpha level below which pixels are considered
+ * transparent.  Should be 127 for 3d where alpha is threshold, but 0 for
+ * 2d where alpha is blended.
+ */
+void imageCleanTransparent(video::IImage *src, u32 threshold);
+
+/* Scale a region of an image into another image, using nearest-neighbor with
+ * anti-aliasing; treat pixels as crisp rectangles, but blend them at boundaries
+ * to prevent non-integer scaling ratio artifacts.  Note that this may cause
+ * some blending at the edges where pixels don't line up perfectly, but this
+ * filter is designed to produce the most accurate results for both upscaling
+ * and downscaling.
+ */
+void imageScaleNNAA(video::IImage *src, const core::rect<s32> &srcrect, video::IImage *dest);